1. Field of the Invention
This invention relates to a head-up display for motor vehicles, in particular to a head-up display having a projector enclosed in a dashboard of a motor vehicle, in which an image of an object is projected through an aperture provided at the top of the dashboard onto a reflecting member such as a front windshield provided in front of the driver's seat of the motor vehicle, whereby a driver can observe the visible information of the image produced thereon.
2. Description of the Prior Art
Referring now to the drawings in FIGS. 1 and 2, the structures of two types of conventional head-up displays are explained.
FIG. 1 shows the basic structure of one of these conventional head-up displays, which has a projector 5 enclosed in a dashboard 1 arranged in front of the driver's seat. The dashboard 1 has an aperture 1a provided at the top of the dashboard 1. The projector 5 comprises a light source 2, a liquid crystal display 3, and a lens 4 covering the aperture 1a . In the projector 5, an image of the liquid crystal display 3 is projected onto the front windshield serving as the reflecting member 7 through the aperture 1a, and a driver 9 can observe a virtual image 6 produced in front of the front windshield 7.
FIG. 2 shows the basic structure of the other conventional head-up display. In this head-up display, a projector 5 is also enclosed in a dashboard 1 which has an aperture 1a provided at the top thereof. The aperture 1a is covered by a transparent cover 11. Although the projector 5 is formed as a unit type, the internal structure thereof is in common with that of the head-up display shown in FIG. 1. The unit type projector 5 is mounted with rotation capabilities with respect to an axis 10 in the dashboard 1, so that it is possible to adjust the position of the image 6 on the front windshield 7 so as to reflect the visual image to a position where the eyes of a driver 9 are normally directed during operation of the vehicle.
In these conventional head-up displays, the aperture la formed on the top of the dashboard 1 is either covered by a lens 4, as in FIG. 1, or by the transparent cover 11 as in FIG. 2 for protecting the lens 4 or for preventing dust from entering into the projector compartment.
In the apertures 1a of both these structures, however, the surfaces of the lens 4 and the transparent cover 11 are usually formed by mirror grinding methods in order to improve the display performance. Therefore, there was the problem that the visibility of the driver is impaired by the reflection of external light entered from the outside, such as sunlight, on the surface of the lens 4 or the transparent cover 11 not only in the employment of the head-up display but also in the unemployment thereof.
In order to overcome this problem, one can conceivably apply antireflection treatment, such as creating fine irregularities or masking, to the surface of the lens 4 or the transparent cover 11. However, such antireflection treatment has, a disadvantage in that it also reduces the quantity of projected light available for display, thereby deteriorating the display capability of the head-up display.